This application is a xc2xa7371 U.S. National Phase application which bases priority on International Application No. PCT/DE00/01842, filed Jun. 7, 2000, which in turn bases priority on German Application No. DE 199 26 182.2, filed Jun. 9, 1999.
1. Field of Invention
The invention relates to a bridge crane having a portal, a boom, a track system laid on the boom and crane trolleys which travel on the tracks.
2. Description of the Prior Art
The problem arises with bridge cranes, particularly container loading bridges, such as are more particularly used for loading and unloading container ships, that if there is only a single track, it is only possible to use in unhindered manner a single trolley. This considerably restricts the capacity of such bridge cranes.
German utility model DE 197 03 282 A1 discloses a container loading bridge in which, besides the working track which guides the trolley extending transversely to said track when the trolley is carrying a load, has a return track comprising a single rail and running laterally alongside the same, and on which the crane trolley extends longitudinally to the direction of travel, the wheel suspension mechanism of the crane trolleys being rotatable about a vertical axis in order to permit the change from the longitudinal orientation to the transverse orientation.
The known system is advantageous compared with the hitherto known proposals, but suffers from the disadvantage that as a result of the use of a single rail for the return track, problems can arise with respect to the running stability.
The problem of the invention is to improve the system known from German Utility Model DE 197 03 282 A1 with respect to the running stability of the crane trolleys to be returned.
According to the invention, this problem is solved by the features of claim 1. Claim 2 gives advantageous developments of the invention.
The invention is described in greater detail hereinafter relative to two drawings of two embodiments of the track system in diagrammatic form. With regards to other details of the bridge crane construction, reference is made to German Utility Model DE 197 03 282 A1.